Advances in 4H-SiC Homoepitaxy for Production and Development of Power Devices
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0911-B09-02
Advances in 4H-SiC Homoepitaxy for Production and Development of Power Devices Bernd Thomas, Christian Hecht, René Stein, and Peter Friedrichs SiCED Electronics Development GmbH & Co KG, Guenther-Scharowsky-Strasse 1, Erlangen, 91058, Germany ABSTRACT In this paper we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system. This equipment exhibits a capacity of 7×3” wafers per run and can be upgraded to a 6×4” setup. Characteristics of epilayers and reproducibility of the processes are reported. Furthermore, we show recent results of p-type SiC homoepitaxial growth on 3” 4° off-oriented substrates using a single-wafer hot-wall CVD. The dependence of layer properties on growth parameters, doping and thickness uniformity as well as doping memory effects are discussed. For the characterization of epitaxially grown pn-junctions first research grade pindiodes were fabricated. The p-type emitters were either deposited in the same growth run together with the n-type buffer and drift layers (continuous growth) or the n- and p-layers were grown in two different growth runs (separate growth). INTRODUCTION During the last years significant progress in bulk and epitaxial growth of 4H-SiC could promote the commercialization of SiC power devices like Schottky Barrier Diodes (SBD) with blocking voltages from 300 V to 1200 V. The costs could be reduced by enlarging the wafer size as well as by transferring epitaxial growth from single-wafer to multi-wafer CVD systems. Besides good material properties like crystal structure, purity and specular surface morphology it becomes more and more necessary to achieve excellent values in homogeneity of doping and thickness as well as excellent run-to-run and intra-run reproducibility in order to meet the requirements of production needs. Bipolar diodes, JFETs, MOSFET’s and SIT’s are currently under development. Epitaxial layers for such devices are mostly grown in single-wafer chemical vapor deposition (CVD) systems. Especially devices with blocking voltages >3kV are of great interest for high-power electronics. Bipolar pin-diodes of different blocking voltage classes with implanted emitters have been developed and fabricated at SiCED for several years [1, 2]. In recent years it was shown that pin-diodes suffer from instability problems detected as a drift of the forward voltage (Vf) after stress tests. It could be shown that the Vf-drift is caused by expansion of stacking faults originating from basal plane dislocations [3, 4]. Sumakeris et al. reported that several measures can improve Vf-stability [5]. However, the most effective one is the growth of a thick buffer layer after a selective KOH-etch procedure of the wafer followed by a re-polish of the wafer surface. The growth of epitaxial p-type emitters in continuous growth runs additionally improves the stability of pin-diodes. In the first part of this paper, we present results of epitaxial growth performed in a commercial hot-wall CVD multi-wafer reactor for power device
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